The present invention relates to a lamp or a display comprising at least one light panel in the form of an OLED illuminant, lying on or against at least one partially light-permeable carrier plate of the lamp in a planar manner.
Light panels in terms of the above-mentioned definition comprise light-emitting OLED panels (OLED light panels), which can be fitted into lighting systems as well as OLED display panels, i.e. OLED panels which have a display function and are suitable for reproducing stationary images (photos, advertising etc.) or moving images (films, videos etc.).
Organic LEDs, called OLED hereunder, have been known for some years and up to now were used mainly in the display sector. The reason for this is that up till recently the luminous flux emitted by the OLEDs was not sufficient for the purpose of general lighting. Therefore OLEDs could only be used for supplementary lighting or effect lighting. Moreover manufacturing costs of OLEDs, until a few years ago, were very high, to the extent that it was not economic to use them for the purpose of general lighting. Recently however, ever more effective OLEDs with increasing light yield have been developed with production costs steadily decreasing.
Messrs. Philips for example are offering flat OLED panels under the name “lumiblade GL 350”, which for a size of 124.5×124.54 mm deliver a luminous flux of 120 lumen white light, which for example is quite sufficient for a table lamp or other applications in the field of residential lighting (see publication in the internet (http://www.philips.de/lightcommunity/trends/oled/lumibladeoledgl350.wpd.)
With OLED panels of the type mentioned the OLED stack itself is usually arranged on a carrier plate consisting of glass or plastic. If such an OLED panel is to be integrated with a lamp, it is obvious to attach the one or more OLED panels to a light-permeable carrier plate. The problem with this is, however, that when placing the OLED panel against the light-permeable carrier plate, wherein two planar surfaces are in contact with each other, a thin layer of air always forms between these two surfaces. This layer of air has proved to be a nuisance due to the fact that during light extraction from the flat OLED panel into the flat carrier plate the loss of light is considerable, a fact which is due to the layer of air between the flat OLED panel and the flat carrier plate, which comprises a refractive index different from that of the carrier plates. This negative effect is present both when surfaces are directly placed together and when both surfaces are treated, for example, with a diffuser layer through matting, structuring or applying a film. The loss of light is due to reflection or total reflection between the two planar elements.
One objective of the development on which the present invention is based therefore consisted in urging this layer of air out of the way and in replacing it by a refractive index which is as close as possible to that of the planar carrier plate.
In principle it would be possible to glue the light panel flat against the light-permeable carrier plate, which however is technically difficult. On the one hand this leads to air inclusions, and on the other to a loss of light due to the adhesive layer between the two planar elements. A further disadvantage consists in the fact that as a result of gluing the light panel onto the light-permeable carrier plate of the lamp, the light panel can no longer be detached from the carrier plate of the lamp. For inspection purposes however, a separable connection would be advantageous.
The older publication DE 10 2012 214 478 A1 not pre-published relative to the present application has disclosed an elongated light module with sealed luminous band, which comprises a first lower partial region consisting of an LED band on a circuit board, which is sealed into a polymer compound. A thin adhesive layer is applied to the top of this lower partial region. Further, a second partial region is provided, which forms a diffusely reflecting light-permeable body and consists of a polymer compound such as a silicone. The bonding agent for connecting the two partial regions may be a liquid silicone. During the manufacture of this lamp module however, the two partial regions are heated, then the adhesive layer is applied to one of the partial regions, then both partial regions are joined face to face, followed by the entire assembly being heated e.g. in an oven. In this way a permanent material bond is created between the two partial regions, which cannot be undone. The lower partial region, in which the LEDs are sealed, consists of a light-impermeable polymer compound, since light emission is intended only in an upward direction in the area of an emitter surface of the polymer compound so that the light is emitted into the light-permeable body of the second partial region.
In the DE 11 2011 104 636 T5 a light-emitting assembly with a plurality of electroluminescent elements with a substrate is described. This known light-emitting device is very thin, film-like and flexible and can therefore serve as a planar illuminant which is applied to the curved surface of the lamp shade of a lamp or can be used as a kind of luminous wallpaper on a wall. During layer construction a synthetic resin layer may also be applied to a substrate serving as a carrier for the film, wherein instead of a synthetic resin a liquid with a high index of refraction may be used. After deposition this layer is however hardened by heat or light so that a material bond is formed between the substrate and the light-emitting layers. A sealing layer is then applied onto the top of the layer assembly of the light-emitting layers in order to protect the functional layers. Following manufacture the substrate and the layers applied to it form an inseparable unit, which is used as a luminous film, and no provision is made, nor would it be meaningful to provide for a separation between the substrate (of the carrier layer) and the functional layers, because this would mean a destruction of the product.
The DE 20 2009 016 123 U1 describes an electroluminescent film composite, in which an electroluminescent element is applied to a glass or a plastic film as a carrier, wherein the element is permanently attached to the carrier substrate by means of an adhesive layer, which covers the same on the top and overhangs on the edges. Above the electroluminescent element there extends a protective film laminate, which is also held fast by the adhesive layer on the carrier substrate. The adhesive layer used may consist, for example, of a hot-melt adhesive. A refractive index of 1.40 to 1.52 for the adhesive layer is cited. This known product too is a permanent film composite wherein it is not envisaged that the connection between the carrier substrate and the electroluminescent element could again be undone. Rather provision is made for the topside of the film composite glued to the substrate to be effectively cleaned, because the composite is provided for use in external areas, such as for gluing onto cars. It would therefore be counter-productive if the carrier substrate separated from the electroluminescent element during cleaning, as this would lead to a destruction of the luminous film.